1. Field of the Invention
The present disclosure relates generally to an optical apparatus, and more particularly, to an optical system for a beam projector that magnifies an image picture output from a display panel and projects the magnified image picture to a screen.
2. Description of the Related Art
A beam projector is a light instrument that facilitates the implementation of a large image picture using an optical system and a display panel. The size of the image picture can be adjusted according to a distance between the beam projector and a screen. If it is possible to secure a sufficient distance to the screen, it is easy to implement a large image picture having high definition regardless of the size of the display apparatus.
An optical system in a beam projector structure may be classified into an illumination optical system and a transmissive optical system. The illumination optical system represents an optical system formed by optical components arranged from the light source to the display panel, and the transmissive optical system represents an optical system formed by optical components arranged from the display panel to a projection lens configured to project an image. In operation, a light produced from the light source progresses through the illumination optical system to be incident on the display panel, and an image picture implemented on a display panel progresses through the transmissive optical system to be finally projected to the outside of the beam projector through a transmissive lens.
Typically, a projection optical system magnifies an image picture implemented on a display panel and projects the image picture to a screen. The definition of the image picture can be selectively adjusted through focusing. The illumination optical system makes red, green, and blue lights individually incident on the display panel. Light-emitting diodes are used to provide a light source in configuring an illumination optical system, thereby remarkably improving the color reproduction of the beam projector. Furthermore, a product using laser diodes as a light source has been proposed. U.S. Pat. No. 8,167,440 (registered on May 1, 2012) discloses a structure in which light emitting diodes and laser diodes are combined as a light source of an illumination optical system. The illumination optical system disclosed in the U.S. patent uses a combination of a laser diode emitting a blue laser light and a light-emitting diode emitting a red light as a light source, and the red, green and blue lights progress along different paths, respectively, to arrive at the display panel.
Recently, technical developments are made to miniaturize such a beam projector to be equipped in a portable terminal, such as, for example, a mobile communication terminal, a portable computer, a multimedia player, and a compact digital camera. With this implementation, it becomes possible to project a data or a moving picture stored in a portable terminal equipped with a beam projector.
The miniaturization of a display panel and an optical system is essentially required to configure a miniaturized beam projector. A compact flat device, such as a DMD (digital micro-mirror device) and an LCoS (liquid crystal on silicon) has been developed as a display panel and is applied to a beam projector. However, as described above, although an illumination optical system is improved in color reproduction by using a plurality of light-emitting diodes and/or laser diodes, lights progress along different paths in the illumination optical system depending on the colors of the lights to be incident on the display panel which requires a plurality of optical components, for example lenses and mirrors. A plurality of light sources and these lenses and mirrors are arranged on the different optical paths which are difficult to miniaturize when implemented in a portable terminal.